Annual average PM2.5 exposure level in Delhi is 110 µg/m3, much higher than the WHO limit of 5 µg/m3, the report found. Photo: Wikimedia Commons

Delhi and Kolkata have the highest PM2.5 pollution in the world: Report

Indian and most global cities far exceed WHO’s air pollution guidelines for two major health pollutants, posing serious health risks, says the report

According to a new report, Indian cities of Delhi and Kolkata have the worst PM2.5 levels in the world. While the World Health Organisation (WHO) air quality guideline is 5 µg/m3 for PM2.5, the report, published by the US-based research organisation Health Effects Institute (HEI) found an annual average exposure level in Delhi at 110 µg/m3 and in Kolkata at 84 µg/m3. 

The report, Air Quality and Health in Cities, released by the State of Global Air Initiative, analysed air pollution and global health effects for more than 7,000 cities around the world, focusing on two of the most harmful pollutants; fine particulate matter (PM2.5) and nitrogen dioxide (NO2). 

Human sources of PM2.5 include household burning, energy production and use, industrial activities, vehicles, etc. Nitrogen dioxide (NO2) is a gaseous pollutant and a key marker of traffic-related air pollution. Particularly abundant in cities and urban areas, NO2 and other nitrogen oxides can also react with other chemicals in the air to form particulate matter and ozone. Combustion of fossil fuels in vehicles, energy production, and industries is the leading source of NO2. While PM2.5 pollution tends to get more attention on known hotspots around the world, less data has been available for NO2 at this global scale. NO2 also has a shorter lifetime compared with PM2.5 and other air pollutants.

The top 10 most polluted cities for both PM2.5 and NO2, among most populated cities in 2019. WHO Air Quality Guidelines are 5 µg/m3 for PM2.5 and 10 µg/m3 for NO2. Source: Air Quality and Health in Cities

Health Impacts 

According to the report, exposure to air pollution is linked to increased hospitalisations, disability, and early death from respiratory diseases, heart disease, stroke, lung cancer, and diabetes, as well as communicable diseases like pneumonia. Worldwide, air pollution is responsible for one in nine deaths, accounting for 6.7 million deaths in 2019, with particularly strong impacts on the young, the elderly, and those with chronic respiratory and heart diseases.

Among the most populous cities in each region (N = 103), the top 20 with the highest PM2.5-related disease burden in 2019. Source: Air Quality and Health in Cities

In 2019, 1.7 million deaths linked to PM2.5 exposure occurred in the 7,239 cities included in the analysis, with cities in Asia, Africa, and Eastern and Central Europe seeing the greatest health impacts. In 2019, 86% of the more than 7,000 cities included in this report exceeded the WHO’s 10 µg/m3 guideline for NO2, impacting about 2.6 billion people.

Ambient PM2.5 is the largest driver of air pollution’s burden of disease worldwide. Long-term exposure to PM2.5 pollution is associated with illness and early death from a variety of diseases, including ischemic heart disease, lung cancer, chronic obstructive pulmonary disease (COPD), lower respiratory infections (such as pneumonia), stroke, Type 2 diabetes, and adverse birth outcomes, said the report.

Inhaling high levels of NO2 in a short time can irritate the airways and aggravate existing respiratory diseases. For people with asthma, NO2 exposure has been associated with more frequent and severe symptoms and a greater risk of hospitalisation. The report mentioned that a strong link was also found between traffic-related air pollution and lung cancer mortality, asthma onset in children and adults, and acute lower respiratory infections in children.

By the year 2050, as much as 68% of the world’s population is expected to live in urban areas. This rapid urbanisation places the world’s top cities at the forefront in the battle to reduce the health effects of air pollution, especially in low- and middle-income countries.

The report also highlighted data gaps in low- and middle-income nations, a key aspect to understanding and addressing the health effects of air pollution. According to the WHO’s Air Quality Database, only 117 nations currently have ground-level monitoring systems to track PM2.5, and only 74 nations are monitoring NO2 levels.

Dr. Susan Anenberg of George Washington University, one of the project collaborators, said, “Since most cities around the world have no ground-based air quality monitoring in place, estimates of particulate and gas pollution levels can be used to plan air quality management approaches that ensure the air is clean and safe to breathe.” 

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